Since its introduction, magnetic resonance imaging (MRI) has provided physicians and clinicians with an unparalleled window into the human body. Using a magnetic field in combination with radio waves, MRI produces detailed images of internal organs and body systems, without subjecting a patient to the radiation incurred during traditional x-ray or CT scan procedures. A strong magnet contained in an MRI scanner generates a field which causes molecules in the body to align. The molecules are briefly excited by radio waves as they return to their original condition. During this process, the molecules emit signals that are received and converted into images by a computer. The procedure itself is painless and, in some cases, may eliminate hospitalization for other diagnostic testing and costs associated therewith. The MRI procedure itself is quite safe—the imaging does not damage body tissues.
Despite the apparent advantages of MRI, the potential for interaction between the MRI scanner and ferrous metal objects, either internal or external to the patient, is cause for concern. For example, the MRI magnet (typically 5,000 to 20,000 Gauss, although magnets as strong as 30,000 Gauss are now available) may move internal objects such as metal pins or plates within a patient's body, and may interfere with the functioning of a pacemaker. External metallic objects ranging from hairpins to crash carts have been projectilized by the magnetic field of MRI scanners, causing injury, and even death, to patients undergoing the procedure and to attending staff. In one well-publicized 2001 accident, a six year-old boy undergoing MRI was killed when an oxygen tank was pulled into the bore of the scanner. When brought within reach of the magnetic field, the oxygen tank flew into the scanner and fractured the boy's skull, causing a fatal cerebral hemorrhage.